Hey guys, thanks to an anonymous tip, we have a much more accurate translation of the Trailer Quotes at S.E party, which gives a better hint to the next game!

"-Their wounds cannot be healed. (or I have to go heal their wounds).
-If you get lost in the darkness, join your hands together like before.
-I am counting the days since my birth.
Has the number of days been recorded?
I don't want to forget what has happened since my birth.
-With whose heart does a new story lie? (or "With whose heart does the
next story lie?) = Sora, Terra, and Roxas collage in background.
-Movie using scenes from the secret movie (Sleep By Birth?) with a
rearranged "The Other Promise" playing in the background."

Moving on... a UK Article scan has appeared which talks about Kingdom Hearts II FM+. It's pretty much stuff we already know. However, it does say it will be released in Autumn 2007, but don't take this as a direct confirmation, as Square-Enix has yet to confirm it themselves:

Secret Movie Takes the Mickey
A fresh Kingdom Hearts game is coming and it won't be just another episode, but an entirely new chapter in KH history - that's the message from legendary director Tetsuya Nomura. Having finished his work with Chain of Memories and Kingdom Hearts II: Final Mix, Tetsuya Nomura has revealed he is already working on another Kingdom Hearts game. But he's very firmly avoiding the word 'sequel', and instead pushing the phrase 'a new series'.
To see what this new series will be like, you can unlock a secret CGI trailer in Kingdom Hearts II. To do so, if you're playing on Standard mode, you must unlock everything in Jiminy's Journal. If you're hard enough to take on Proud mode, you only have to complete the worlds (including 100 Acre Woods and Atlantica).

Mouse Mystery
When you've successfully unlocked the movie, an icon of Mickey Mouse's head will appear in your Start menu.
The gorgeous animation sequence is loaded with includes about what KHfans can expect from the next game. The most significant moment appears to be the three fully armoured mystery warriors picking up Sora's, Riku's and Mickey's Keyblades. And then scrapping it out in a field of these mystical weapons.
In an interview with the official KH website, Tetsuya has already confirmed that these masked fighters aren't our three heroes, but of course that doesn't mean that there aren't connections...
As for the Keyblades, he implies that there was a Keyblade War, and goes on to suggest that this new series will answer questions about their ancient weapons raised in Kingdom Hearts and Kingdom Hearts II. There is also a longer secret movie at the end of Kingdom Hearts II: Final Mix, continue where the previous one leaves off.
But Final Mix won't be out in the West until late Autumn 2007, so you'll have to be patient. Or, ahem, watch it on YouTube."

Once again DON'T TAKE THIS AS A CONFIRMATION